CSS background images work very similar to the background command in html. When applied within the <body> tag it will
the image will repeat and fill the entire page. This may seem redundant to the
background tag, however since the background tag is typically applied to each page and CSS are usually linked throughout a site, you can easily in one place, change the backgrounds to many pages similar to what Yahoo.com did recently for breast cancer awareness or what Excite.com seems to do every Halloween.